HEF1/NEDD9/Cas-L (HEF1) is a molecular scaffolding protein that mediates cellular signaling from focal adhesions during interphase and at centrosomes during mitosis. Over the past two years, alterations in expression of HEF1 have been shown to play a significant role in cancer metastasis. Increased expression of HEF1 has been shown to induce invasion in glioblastoma and promote melanoma and lung carcinoma metastasis in humans and mice. Perturbations of HEF1 expression have also been linked to breast cancer metastasis. More than 70% of cases of epithelial ovarian cancer (EOC) are diagnosed at advanced stage, when disease has spread (metastasized) beyond the ovary. While ovarian cancer patients often initially respond well after surgical debulking and chemotherapy, most suffer disease recurrence and ultimately succumb to metastatic disease. Recent studies have shown that HEF1 is commonly overexpressed in advanced stage serous EOC, the most common type of EOC. Importantly, several oncogenic proteins that are activated by HEF1 have also been shown to be activated or overexpressed in EOC. Among these are focal adhesion kinase (FAK), Src and signal transducer and activator of transcription 3 (STAT3). An association of HEF1 overexpression to activation of FAK, Src and STAT3 in ovarian cancer has not yet been established. The goal of this proposal is to understand the cellular mechanisms by which HEF1 overexpression influences ovarian carcinoma development, progression and metastasis and ultimately to validate HEF1 and the signaling pathways activated by HEF1 as targets for therapeutic intervention in ovarian cancer patients. This proposal has three aims. In Aim 1 we will use inducible HEF1/Hef1 expression constructs and RNA interference (RNAi) strategies to determine the effects of enforced expression or depletion of endogenous human HEF1 or murine Hef1 in human and murine ovarian carcinoma cell lines. This aim will also investigate the role of HEF1 in regulation of STAT3 activation and STAT3-mediated migration and invasion. In Aim 2, we will use in vivo mouse model systems to determine the specific requirement(s) of Hef1 expression in tumor cells and/or the tumor microenvironment in EOC development, progression and metastasis. In Aim 3, we will comprehensively evaluate HEF1 and its critical binding partners relevant to cell migration and invasion (e.g., FAK, pFAK, Src, pSrc, STAT3 and pSTAT3) in primary human ovarian tumors. Using human EOC tissue microarrays, we will determine the patterns and relationship of expression of these proteins in normal ovaries as well as in borderline, early and late stage tumors of each histologic subtype (e.g., serous, endometrioid, mucinous and clear cell cancers) and correlate these patterns with clinical data including pathology, treatment and outcome.